Truck & Off-Highway Engineering - October 2021 - 27

POWERTRAIN FEATURE
CFD analysis model for single-passage simulations.
improvement by reducing the nozzle loss especially
at low mass flow operation.
Second, a high-pace design optimization was conducted
for the nozzle vanes, consisting of single passage
CFD simulation (low fidelity) with one nozzle
vane and one turbine blade. Third, the best design was
then modelled completely with turbine housing, and
transient rotor CFD was conducted to evaluate the
stator-rotor interaction (high fidelity). Lastly, these
characteristics were verified on a test bench by conducting
performance and tip timing tests.
CFD simulations were conducted on ANSYS CFX
version 19.1 using a RANS-SST turbulence model with
automatic wall functions setting.
Testing the new design
The test sample for the new VGT nozzle assembly with
3D vanes was tested along with the new rotor to measure
performance and reliability characteristics at the
final phase of development. Turbine efficiency was
measured on a gas stand by replicating the same operating
conditions as the steady-state CFD simulations.
Four pressure sensors and one thermocouple were installed
each at the inlet and outlet to obtain the data for
calculating efficiency, whereas mass flow was measured
using an orifice located upstream of the inlet.
The efficiency calculated from the gas stand measurements
over the entire operation range of the VGT
turbine shows that the new design successfully
achieves about 7% higher efficiency than the base design
at low mass flow region. Also, the peak efficiency
corresponding to HEP operating condition is increased
by approximately 4% and 2% at expansion ratio (ER)
1.5 and ER 2.0, respectively. The maximum mass flow
range of the new turbine lies completely within the
TRUCK & OFF-HIGHWAY ENGINEERING
Nozzle assembly with new vane design: (a) Drive mechanism for moving the
vanes; (b) Use of spacers to maintain vane side clearance; (c) Vanes at minimum
opening angle; (d) Vanes at maximum opening angle.
Setup for tip-timing test.
engine operation range, with a higher efficiency over most of the
region. This indicates that the new design will prove effective in reducing
engine emissions by providing an oxygen-rich environment
for efficient fuel combustion.
The vibration characteristics of the new VGT rotor were measured at
the same test facility as that for performance testing, in addition to using
the combustor installed upstream of the turbine inlet to increase the
October 2021 27
Truck & Off-Highway Engineering - October 2021

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